The use of composite materials formed from fine fragments of desired materials is well known. The uses of these materials are known, though new applications are continually being found. However, the technology is relatively new and there are significant gaps in the prior art.
For instance, while many composite blends are known, many areas still remain to be explored and experimented with. Similarly, the techniques and methods of preparing composites and their pre-cursors are also incomplete, despite being relatively well established in some areas. Consequently, one object of the present invention is to extend the range of knowledge within this field, as well as attempting to increase the number of choices to users of the technology.
Metal Matrix Composites (MMCs) are composites of a tough conventional engineering alloy and a high strength second phase material, which may be an oxide, nitride, carbide or intermetallic. Oxide Dispersion Strengthened (ODS) alloys come at one end of the spectrum of MMCs. These are composites of a tough engineering alloy and a fine dispersion of an oxide. Typically, in order to obtain the required dispersion, there must be no more than 10% volume fraction of the oxide second phase, which may have a size of 10's of nm. At the other end of the MMC spectrum are the CERMETS in which the "second phase" exceeds 50% of the volume fraction, i.e. the oxide, carbide, nitride or intermetallic, in fact, forms the primary phase and the metal is the secondary phase.
Titanium alloy metal matrix composites reinforced with ceramic particulate are known, though traditionally these are usually produced by using conventional and known powder metallurgy techniques. In the known powder metallurgy routes, titanium alloy powder is blended with ceramic powders such as aluminium oxide powders. This blending is usually performed using a low energy ball milling process. The powder mixture is then cold compacted and sintered to produce bulk titanium alloy matrix composite.
However there are several disadvantages associated with the prior art. Firstly, it is a requirement that the titanium or titanium alloy powders are prepared according to a separate and known method. This can be relatively expensive and must be performed independently of the composite forming process. In contrast, ceramic powders are readily available so this does not represent a problem for the prior art. However, the range of available particle sizes of the ceramic powders does represent a problem. Typically, economic manufacturing processes of the ceramic powders is limited in that the smallest readily available powders are in the micrometer size range. While this is adequate for most composites, it is now recognised that smaller sized ceramic particles, or proportions of smaller sized ceramic particles, can improve the physical and mechanical characteristics of the composite product. By way of example, this is now well known in concrete technology which uses exceptionally finely sized silica fume particles to increase the overall strength and durability of the resulting cement/concrete matrix.
U.S. Pat. No. 5,328,501 (McCormick) discloses a process for the production of metal products by subjecting a mixture of one or more reducible metal compound with one or more reducing agent to mechanical activation. The products produced are metals, alloys or ceramic materials which this specification states may be produced as ultra-fine particles having a grain size of one micron or less. A variety of specific reactions are given by way of example, but in all cases, the method is dependent on the mechanical process producing the required reduction reaction. Furthermore, the patent is not directed towards the production of metal matrix composites reinforced with fine ceramic particulate.
There is no disclosure of titanium/alumina composites, nor of any methods for producing such composites.
There are some significant limitations in the prior art which increases the expense of producing composite materials, and which also limits the physical and mechanical characteristics of the composite product.
It is a further object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.